This invention relates to the art of bonding metals, plastics, and other material by the application of mechanical vibratory energy in the ultrasonic frequency range. The bonding may be accomplished with or without the independent application of heat. This bonding process itself is well known and is not part of this invention, but if background information is desired reference may be made to U.S. Pat. Nos. 2,946,119 and 3,002,270 for representative apparatus for performing this bonding technique.
This invention is directed to an electrical supply for providing the power to be transformed by the apparatus into mechanical vibratory energy. The frequency of the electrical output signal of the power supply determines the vibrational frequency of the apparatus. Thus, automatic control of the vibrational frequency may be accomplished by controlling the power supply frequency. It is known that maximum efficiency in energy transformation occurs when a device is being driven at or near its natural mechanical resonant frequency. The resonant frequency varies with several characteristics of the applied load and with environmental conditions, so that it is not sufficient to establish a fixed frequency for the power supply. Instead, it has been found advantageous to provide automatic variation and control of the power supply frequency in order to constantly operate at or near the mechanical resonant frequency.
Other solutions to the problem of providing automatic frequency control have been employed in the past. In U.S. Pat. No. 3,002,270 there is disclosed a power supply in which frequency control is accomplished by a phase comparison of the voltage and current vectors of the power supply output signal. In U.S. Pat. No. 3,889,166 there is disclosed a power supply which provides automatic frequency control by comparing the power supply output signal to a signal generated by an independent set of piezo electric crystals on the mechanical device.
This invention is directed to providing automatic frequency control of the power supply output to maintain operation near the mechanical resonant frequency in a novel and improved manner. It is desired to accomplish this frequency control without the additional circuitry necessary for detection of phase differences, and likewise without the necessity of providing an independent set of piezoelectric crystals on the mechanical vibrating member. While the above are the major objectives of this invention, other objectives will become apparent on reading the specification that follows.